1. Field of the Invention
The present invention relates to a discharge lamp lighting device for supplying a starting waveform required at the start-up of a discharge lamp to the discharge lamp and a technique for causing the reduced loss to the device.
2. Description of the Related Art
Recently, a start-up voltage for lighting a lamp at its lighting start-up has become low owing to the development in technique for a lamp as a discharge lamp. As a result, a waveform required in the discharge lamp lighting device at its start-up has undergone changes.
Conventional discharge lamps needed a high voltage as high as around 15 kV at the lighting start-up and hence a discharge lamp lighting device also needed to be designed, accordingly. By encapsulating krypton or the like inside a discharge lamp, however, a voltage required for the lighting start-up has decreased to around 3 to 5 kV. Further, a discharge lamp lighting device capable of continuously generating a pulse voltage around 1 to 2 kV has been required in order to meet new needs.
In association with such a decrease in lighting start-up voltage of a discharge lamp, the conventional lighting devices have met the above-mentioned needs by applying and developing the conventional high-frequency start-up system. Specifically, as disclosed, in Japanese patent publication No. 2006-513539 (International publication No. WO2004/064457), with the conventional circuit system unchanged, the frequency of an inverter at the lighting start-up is allowed to sequentially change and a resonant frequency is mixed into variations in properties of circuit parts to temporarily obtain a desired pulse voltage, or otherwise, a new circuit is added to the original one to realize the desired pulse voltage.
According to any of the conventional arts proposed in the above publication, etc., it is possible to obtain a desired pulse voltage matching the discharge lamp. However, because an inverter is allowed to operate at such high frequencies as on the order of 70 to 200 kHz, there have been concerns about an increase in internal loss of the discharge lamp lighting device and an inner generation of an unexpected high voltage and/or high current.
Further, whilst an inductor for applying a high voltage pulse to a discharge lamp at the lighting start-up is connected with an output of the inverter, there is a concern that such inductor for applying the high voltage pulse may be magnetically saturated depending on the operational timing of switching elements making up the inverter.
Therefore, with the view of the above problems, it is an object of the present invention to provide a discharge lamp lighting device in which an inductor connected with an output of an inverter can be prevented from being magnetically saturated and besides its internal loss can be reduced to a minimum without adding any parts.